A complete set of golf club irons typically includes a set of eleven irons numbered from 2 (long) through 9 (short), a pitching wedge (PW) and a sand wedge (SW). A 1-iron is also sometimes included in the set, although the average golf club set does not include a 1-iron due to difficulty in using the club. Each iron comprises a head including a hosel and a shaft which is attached to the head by fitting the shaft into a bore of the hosel. The hosel is integrally formed as part of the head. The head also includes a heel, a bottom sole, a toe, a planar striking face, and a back side.
The typical eleven irons of a golf club set have varying degrees of loft angle. The loft angle of an iron is the angle between a vertical plane, which includes the shaft, and the plane of the striking face of the iron. The loft angle effects how much loft is imparted to the ball when it is struck by the tilted, striking face.
Longer-hitting irons (i.e., #2, #3, #4) have progressively longer golf club shafts than the shorter-hitting irons (i.e., #5, #6, #7, #8, #9, PW, SW). Typically, the length of the golf club shaft progressively increases in length from PW through the 2-iron. Further, it is a typical design criteria that each golf club within a set have the same substantially identical swing weight. As the volume of shaft is different for each club due to varying length, the mass of the club head is varied inversely to the length of the shaft such that a substantially constant swing weight is achieved for each club within a complete set. Accordingly, typically the PW head is heaviest and the 2-iron head is lightest within a given set 2-iron through PW. Such is typically provided for in the prior art by making larger hitting face area short irons, and comparatively smaller size hitting face area in the longer irons. The hitting area progressively increases in going from the long irons to the short irons within the typical prior art set.
Golf clubs within a complete set also typically have varying degrees of lie angle throughout the complete set. The lie angle of an iron is the angle between the shaft and the ground (horizontal plane) when the tangent to the sole directly under the head's center of mass is in a horizontal plane and when the shaft lies in a vertical plane. Varying lie angles are provided to accommodate the different length of shafts throughout a complete set of irons. For example, when a golfer addresses the ball with a club, he/she will be standing further away from the ball when hitting with a 2-iron than he/she will when hitting with, for example, a 9-iron, due to the increased length of the 2-iron shaft versus the 9-iron shaft. It is a general prior art goal that the sole of a golf club head lay flat against the turf when the ball is addressed by the golfer. Accordingly, the hosel angles downwardly from vertical for the longer irons than is required for the shorter irons.
Dynamics of the shaft during swinging the golf club can, however, have an adverse effect with respect to the above relationship. Specifically, the shaft of a longer distance iron (i.e., #2, #3, #4 and #5) creates more club head speed and is more flexible due to the longer length of the shaft. This actually results in a curving or banana-like bending of the shaft slightly inward and down at impact, thus forcing the toe of the club slightly down and into the ground, as opposed to passing parallel relative thereto. Thus a golf club head, especially of a long iron, leaves the toe vulnerable even for a correct swing to being pulled downwardly open by the ground at ball impact. This will tend to cause the ball to fade right or slice right, for a right-handed golfer. The average golfer has a considerably more difficult time in consistently hitting the longer distance irons than he/she does hitting the shorter distance irons because of these dynamics in controlling a longer shaft.
There are common or standard lie angles provided for a golf club head throughout a complete set for an average height golfer. A prior art example is shown in Table 1 below, with the numbers referring to the angle upward from horizontal.
TABLE 1 Prior Art Lie Angle (Degrees) #2 58 #3 59 #4 60 #5 61 #6 62 #7 62.5 #8 63 #9 64 PW 65 SW 66
To accommodate different height golfers, a different average golf club length is used within a given correlated complete set. A variation might also exist for an average height golfer if he/she squats more in their stance versus stands upright. The prior art in accommodating for such varying golfers merely changes this standard angling range a given constant angle through the set. For example if a golfer needs a more upright lie, such as a 2.degree. upright, the prior art heads would typically make all the irons in the given set 2.degree. more upright (i.e., going from 60.degree. for a 2-iron through, say, 67.degree. for the PW with the above scale). However when this is done, the shorter distance irons (i.e., #7, #8, #9 and PW) become too upright. The shorter irons do not create as much club head speed because the shaft length is shorter, which makes them stiffer and decreases the inward and downward flex of the shaft. The golfer will therefore have a tendency with such a set to pull or hook the ball left, for a right-handed golfer. The golfer will also tend to stand very close to the ball to get the sole of the club to lay flat at address, putting the golfer in an awkward and improper position. This becomes especially vivid when, for example, a tall person needs a 4.degree. upright adjustment to get the toe out of the ground on long-distance irons. Such would make the prior art pitching wedge according to the above scale provided at 69.degree. upright, essentially making that club unplayable.
Needs remain in golf club iron head design to better facilitate a golfer's control in hitting with the long irons.